For example, a phenomenon called “smear” occurs in a camera module including a CCD (Charge Coupled Device) as an image pickup element. The smear is a phenomenon in which a photographed image has a white zonate part in a case where (i) a subject to be photographed bears intense light such as the sun light or electric light and (ii) the intense light enters the image pickup element. The smear occurs due to a successive overflow of electric charge in the CCD. More specifically, when a light receiving element (pixel) of the CCD receives the intense light, the electric charge overflows in a part of the light receiving element. While the electric charge is moving among light receiving elements, a chain of overflows of electric charge occurs, thereby causing the smear.
In order to prevent the smear, a camera module often includes a mechanical shutter. The mechanical shutter shuts out the intense light which causes the smear before the smear occurs, thereby preventing a smear.
For example, Patent Literatures 1 through 3 disclose mechanical shutters for respective camera modules. FIG. 9 is a cross-sectional view of the camera module disclosed in Patent Literature 1. FIG. 10 is a cross-sectional view of the mechanical shutter disclosed in Patent Literature 2. FIG. 11 is a plain view of the mechanical shutter disclosed in Patent Literature 3.
More specifically, as shown in FIG. 9, a camera module 110 of Patent Literature 1 is arranged so that components such as a transparent plate 112, an image pickup optical system 113, an image pickup element 114, a substrate 115, and shutter fins 116 and 117 are stacked in an optical axis direction. A shutter actuator 118 for electromagnetically driving the shutter fins 116 and 117 is further provided on one side of the image pickup optical system 113.
Moreover, as shown in FIG. 10, a mechanical shutter 120 for a camera module disclosed in Patent Literature 2 is arranged so that a recessed part 121 in its center and shutter fins 122 and 123, an aperture fin 124, and drive mechanisms 126 and 127 for driving an auxiliary fin 125 are provided, in a dispersed manner, on both sides of the recessed part 121. Note that Patent Literature 2 is silent about an arrangement of an image pickup optical system such as an image pickup lens.
On the other hand, a mechanical shutter for a camera module disclosed in Patent Literature 3 operates based on the following principle. As shown in FIG. 11, a mechanical shutter 130 includes: a shutter base plate 131; an axis 132; and a rotor 133. The axis 132 is provided on the shutter base plate 131, and the rotor 133 is attached to the axis 132 so as to rotate around the axis 132. The rotor 133 is a bipolar permanent magnet. That is, the mechanical shutter 130 is a moving magnet type shutter driven by the rotor (permanent magnet) 133. The mechanical shutter 130 includes a substantially U-shaped yoke 134 having two leg parts 134a and 134b whose leading ends are respective magnetic pole parts. Further, a bobbin 136, around which a coil 135 is wound, is fit into the leg part 134b. 
According to the mechanical shutter 130, while a current is supplied to the coil 135, a magnetic field generated from the coil 135 acts on the magnetic poles parts (the leading ends of the leg parts 134a and 134b). Then, the magnetic field further acts on the rotor 133 so as to rotate the rotor 133. This causes a shutter fin (not illustrated) to be rotated in conjunction with the rotation of the rotor 133, thereby opening or closing an aperture 137 provided in the center of the mechanical shutter 130. Note that a direction of the magnetic field which acts on the rotor 133 is reversed in accordance with a direction of the current supplied to the coil 135. It follows that the rotor 133 can be rotated clockwise or anticlockwise depending on the magnetic field which acts on the rotor 133.
On the other hand, in these years, cases have been increased in which a camera module having an auto-focus function is employed in a mobile phone. The auto-focus function is achieved by providing a lens drive device in the camera module. The lens drive device encompasses various types such as a VCM (Voice Coil Motor) type, a stepping motor utilizing type, and a piezoelectric element utilizing type. These types of lens drive devices have already been available in the market.
For example, Patent Literature 4 discloses a VCM type lens drive device. FIG. 12 is a cross-sectional view of the lens drive device of Patent Literature 4. The lens drive device 200 includes a holder 202 which holds a lens 201 in the center thereof. Plate springs 203U and 203L are provided on the top part and on the bottom part of the holder 202, respectively. This causes the holder 202 to be supported so that the lens 201 can move in an optical axis direction.
Moreover, a coil 204 is fixed to a flange part of the holder 202. The coil 204 is contained in a yoke 205. A permanent magnet 206 is provided on an inside face of the yoke 205 so as to face the coil 204 while being away from the coil 204. This arrangement makes it possible to drive the lens drive device 200 by use of electromagnetic force.
On the other hand, three projections 208 are formed on a base 207. In the assembly work state of the lens drive device 200, the projections 208 support the holder 202.
A cover 209 is provided above the yoke 205. The cover 209 and the base 207 have apertures 210 and 211, respectively, in the centers thereof. The apertures 210 and 211 are provided for passing through light.
However, the camera module including the moving magnet type mechanical shutter and the VCM type lens drive device has a problem that the camera module cannot prevent generation of a smear completely.
More specifically, as described above, according to the mechanical shutter 130 illustrated in FIG. 11, the rotor 133 is rotated by the magnetic field which acts on the magnetic pole parts while the current is being supplied to the coil 135. Further, the shutter fin opens or closes the aperture (light path) 137 in conjunction with the rotation of the rotor 133.
However, in a case where the camera module includes the VCM type lens drive device 200 as well as the mechanical shutter 130, both the mechanical shutter 130 and the lens drive device 200 are to be driven by electromagnetic force. It follows that a magnetic field leaked from the lens drive device 200 also acts on the mechanical shutter 130. As a result, the magnetic field adversely affects the operation of the mechanical shutter 130.
More specifically, it is assumed that a magnetic field 138, which points from the leading end of the leg part 134b toward the leading end of the leg part 134a, acts on the magnetic pole parts. The mechanical shutter 130 shuts out intense light which causes a smear, thereby preventing generation of the smear. The magnetic field 138 is set so that the light causing the smear is shut out. This can be realized by supplying a predetermined current to the coil 135 so that the shutter fin operates at a predetermined speed.
However, while the magnetic field is being leaked from the lens drive device 200, the magnetic field acts on the magnetic field 138. This prevents normal operation of the mechanical shutter 130. It follows that the closing operation of the shutter fin for the aperture 137 is likely to be carried out at a speed slower than the predetermined speed. Thus, the problem occurs that the generation of the smear cannot be prevented completely.